Method of forming an optimized fiber reinforced liner on a rotor with a motor

ABSTRACT

A method of forming a rotor for a positive displacement motor. The method includes forming a liner that includes at least two resilient layers and at least one fiber layer, and the at least two resilient layers are positioned so as to enclose the at least one fiber layer. The liner is positioned on a rotor tube, and the rotor tube includes a shaped outer surface including at least two radially outwardly projecting lobes extending helically along a selected length of the rotor tube. The liner is cured on the rotor tube so that the liner conforms to the radially outwardly projecting lobes formed on the outer surface and to the helical shape of the outer surface. The curing forms a bond between the liner and the outer surface and between the at least two resilient layers and the at least one fiber layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 10/097,480filed Mar. 14, 2002, now U.S. Pat. No. 6,604,922.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to stators used with positivedisplacement drilling motors. More specifically, the invention relatesto a fiber reinforced liner adapted for use with formed stators.

2. Background Art

Positive Displacement Motors (PDMs) are known in the art and arecommonly used to drill wells in earth formations. PDMs operate accordingto a reverse mechanical application of the Moineau principle whereinpressurized fluid is forced though a series of channels formed on arotor and a stator. The channels are generally helical in shape and mayextend the entire length of the rotor and stator. The passage of thepressurized fluid generally causes the rotor to rotate within thestator. For example, a substantially continuous seal may be formedbetween the rotor and the stator, and the pressurized fluid may actagainst the rotor proximate the sealing surfaces so as to impartrotational motion on the rotor as the pressurized fluid passes throughthe helical channels.

Referring to FIG. 1, a typical rotor 10 includes at least one lobe 12(wherein, for example, channels 14 are formed between lobes 12), a majordiameter 8, and a minor diameter 6. The rotor 10 may be formed of metalor any other suitable material. The rotor 10 may also be coated towithstand harsh drilling environments experienced downhole. Referring toFIG. 2, a typical stator 20 comprises at least two lobes 22, a majordiameter 7, and a minor diameter 5. Note that if the rotor (10 inFIG. 1) includes “n” lobes, the corresponding stator 20 used incombination with the rotor 10 generally includes either “n+1” or “n−1”lobes. Referring to FIG. 3, the stator 20 generally includes acylindrical external tube 24 and a liner 26. The liner 26 may be formedfrom an elastomer, plastic, or other synthetic or natural material knownin the art. The liner 26 is typically injected into the cylindricalexternal tube 24 around a mold (not shown) that has been placed therein.The liner 26 is then cured for a selected time at a selected temperature(or temperatures) before the mold (not shown) is removed. A thickness 28of the liner 26 is generally controlled by changing the dimensions ofthe mold (not shown).

A lower end of the rotor may be coupled either directly or indirectlyto, for example, a drill bit. In this manner, the PDM provides a drivemechanism for a drill bit independent of any rotational motion of adrillstring generated proximate the surface of the well by, for example,rotation of a rotary table on a drilling rig. Accordingly, PDMs areespecially useful in drilling directional wells where a drill bit isconnected to a lower end of a bottom hole assembly (BHA). The BHA mayinclude, for example, a PDM, a transmission assembly, a bent housingassembly, a bearing section, and the drill bit. The rotor may transmittorque to the drill bit via a drive shaft or a series of drive shaftsthat are operatively coupled to the rotor and to the drill bit.Therefore, when directionally drilling a wellbore, the drilling actionis typically referred to as “sliding” because the drill string slidesthrough the wellbore rather than rotating through the wellbore (as wouldbe the case if the drill string were rotated using a rotary table)because rotary motion of the drill bit is produced by the PDM. However,directional drilling may also be performed by rotating the drill stringand using the PDM, thereby increasing the available torque and drill bitrpm.

A rotational frequency and, for example, an amount of torque generatedby the rotation of the rotor within the stator may be selected bydetermining a number of lobes on the rotor and stator, a major and minordiameter of the rotor and stator, and the like. An assembled view of arotor and a stator is shown in FIG. 3. Rotation of the rotor 10 withinthe stator 20 causes the rotor 10 to nutate within the stator 20.Typically, a single nutation may be defined as when the rotor 10 movesone lobe width within the stator 20. The motion of the rotor 10 withinthe stator 20 may be defined by a circle O which defines a trajectory ofa point A disposed on a rotor axis as point A moves around a stator axisB during a series of nutations. Note that an “eccentricity” e of theassembly may be defined as a distance between the rotor axis A and thestator axis B when the rotor 10 and stator 20 are assembled to form aPDM.

Typical stators known in the art are formed in a manner similar to thatshown in FIG. 2. Specifically, an inner surface 29 of the external tube24 is generally cylindrical in shape and the stator lobes 22 are formedby molding an elastomer in the external tube 24. Problems may beencountered with the stator 20 when, for example, rotation of the rotor10 within the stator 20 shears off portions of the stator lobes 22. Thisprocess, which may be referred to as “chunking,” deteriorates the sealformed between the rotor 10 and stator 20 and may cause failure of thePDM. Chunking may be increased by swelling of the liner 26 or thermalfatigue. Swelling and thermal fatigue may be caused by elevatedtemperatures and exposure to certain drilling fluids and formationfluids, among other factors. Moreover, flexibility of the liner 26 maylead to incomplete sealing between the rotor 10 and stator 20 such thatavailable torque may be lost when the rotor compresses the stator lobematerial, thereby reducing the power output of the PDM. Accordingly,there is a need for a stator design that provides increased power outputand increased longevity in harsh downhole environments.

Prior attempts have been made to increase stator durability and heatconduction properties. U.S. Pat. No. 6,201,681, issued to Turner,describes fibers disposed in an elastomer material that forms a statorfor a helicoidal pump or motor. The fibers are generally arranged toform a two or three dimensional structure within the elastomer material.The fibers are either coated with the elastomer material as they arebeing woven to form a fabric layer or are formed into the desiredarrangement to form a fiber skeleton. After the fiber skeleton isformed, elastomer is then injected into the stator under heat andpressure to complete the process.

However, fiber reinforcement has presented manufacturing difficultiesbecause it is difficult to achieve a desired fiber arrangement usinginjection molding techniques. Fiber reinforcement via injection moldingrequires additional manufacturing steps, and the manufacturing processesgenerally produce either a different concentration of fibers per unitvolume of elastomer between the thick portions of the lobes and the thinportions (which reduces the mechanical strength of the liner) or, whenfibers are disposed manually, a different number of layers must beapplied in the thick portions of the lobes as compared to the thinportions.

Accordingly, there is a need for a liner material that is more durableand is able to withstand prolonged sealing engagement between a rotorand a stator in harsh operating conditions. Moreover, there is a needfor a new liner material that is adapted for use with stators thatinclude contoured inner surfaces formed on the stator tube. The linermaterial should be durable and should be less susceptible to wear and,for example, thermal fatigue. The liner material should also be easy toinstall so as to achieve a desired fiber concentration proximateselected regions of the rotor or stator.

SUMMARY OF INVENTION

In one aspect, the invention comprises a method of forming a stator fora positive displacement motor. The method comprises forming a linerincluding at least two resilient layers and at least one fiber layer.The at least two resilient layers are positioned so as to enclose the atleast one fiber layer. The liner is positioned in a stator tube, and thestator tube comprises a shaped inner surface including at least tworadially inwardly projecting lobes extending helically along a selectedlength of the stator tube. The liner is cured in the stator tube so thatthe liner conforms to the radially inwardly projecting lobes formed onthe inner surface and to the helical shape of the inner surface. Thecuring is adapted to form a bond between the liner and the inner surfaceand between the at least two resilient layers and the at least one fiberlayer.

In another aspect, the invention comprises a stator for a positivedisplacement motor. The stator comprises a stator tube and a liner. Thestator tube comprises a shaped inner surface including at least tworadially inwardly projecting lobes extending helically along a selectedlength of the stator tube. The liner comprises at least two resilientlayers and at least one fiber layer, and the at least two resilientlayers are positioned so as to enclose the at least one fiber layer. Theliner is disposed in the stator tube proximate the inner surface, andthe liner conforms to the radially inwardly projecting lobes formed onthe inner surface and to the helical shape of the inner surface.

In another aspect, the invention comprises a positive displacement motorincluding a stator comprising a shaped inner surface. The inner surfacecomprises at least two radially inwardly projecting lobes extendinghelically along a selected length of the stator. A liner comprising atleast two resilient layers and at least one fiber layer is disposedwithin the stator so that the liner conforms to the helical shape formedby the at least two radially inwardly projecting lobes. The at least tworesilient layers are positioned so as to enclose the at least one fiberlayer. A rotor comprises at least one radially outwardly projecting lobeextending helically along a selected length of the rotor. The rotor isdisposed inside of the stator and the at least one radially outwardlyprojecting lobe formed on the rotor is adapted to sealingly engage theat least two radially inwardly projecting lobes formed when the linerconforms to the inner surface of the stator.

In another aspect, the invention comprises a method of forming a rotorfor a positive displacement motor. The method comprises forming a lineron a rotor by layering at least two resilient layers and at least onefiber layer on an outer surface of the rotor. The at least two resilientlayers are positioned so as to enclose the at least one fiber layer, andthe rotor comprises at least one radially outwardly projecting lobeextending helically along a selected length of the rotor. The liner iscured on the rotor so that the liner conforms to the at least oneradially outwardly projecting lobe formed on the rotor and to thehelical shape of the rotor, and the curing is adapted to form a bondbetween the liner and the outer surface and between the at least tworesilient layers and the at least one fiber layer.

In another aspect, the invention comprises a rotor for a positivedisplacement motor. The rotor comprises at least one radially outwardlyprojecting lobe formed on an outer surface of the rotor and extendinghelically along a selected length of the rotor. A liner comprising atleast two resilient layers and at least one fiber layer is disposed onthe rotor proximate the outer surface. The at least two resilient layerspositioned so as to enclose the at least one fiber layer, and the linerconforms to the at least one radially outwardly projecting lobe formedon the outer surface and to the helical shape of the rotor.

In another aspect, the invention comprises a positive displacement motorincluding a stator comprising a shaped inner surface. The inner surfacecomprises at least two radially inwardly projecting lobes extendinghelically along a selected length of the stator. A rotor comprises atleast one radially outwardly projecting lobe formed on an outer surfaceof the rotor and extending helically along a selected length of therotor. A liner comprising at least two resilient layers and at least onefiber layer is disposed on the external surface so that the linerconforms to the helical shape formed by the at least one radiallyoutwardly projecting lobe. The at least two resilient layers arepositioned so as to enclose the at least one fiber layer. The rotor isdisposed inside of the stator and the at least one radially outwardlyprojecting lobe formed when the liner conforms to the outer surface ofthe rotor is adapted to sealingly engage the at least two radiallyinwardly projecting lobes formed on the stator.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross-sectional view of a prior art rotor.

FIG. 2 shows a cross-sectional view of a prior art stator.

FIG. 3 shows a cross-sectional view of an assembled positivedisplacement motor.

FIG. 4 shows a cross-sectional view of an embodiment of the invention.

FIG. 5 shows a perspective view of an embodiment of the invention.

FIG. 6 shows a perspective view of an embodiment of the invention.

FIG. 7 shows a cross-sectional view of an embodiment of the invention.

FIG. 8 shows a cross-sectional view of an embodiment of the invention.

FIG. 9 shows a cross-sectional view of an embodiment of the invention.

FIG. 10 shows a cross-sectional view of an embodiment of the invention.

FIG. 11 shows a cross-sectional view of an embodiment of the invention.

FIG. 12 shows a perspective view of an embodiment of the invention.

FIG. 13 shows a cross-sectional view of an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 4 shows an embodiment comprising at least one aspect of the presentinvention. A positive displacement motor (PDM) 30 comprises a stator 32and a rotor 34. The stator 32 comprises an external tube 38 that may beformed from, for example, steel or another material suitable fordownhole use in a drilling environment. The stator also comprises aliner 36.

The external tube 38 comprises a shaped inner surface 44 that comprisesat least two lobes 46 formed thereon. The lobes 46 are helically formedalong a selected length of the external tube 38 so that the lobes 46define a helical pattern along the selected length. The helical form ofthe inner surface 44 generally corresponds to a desired shape for statorlobes. The liner 36 typically comprises at least two lobes 40, and athickness 42 of the liner 36 may be either uniform or non-uniformthroughout a cross-section thereof. Accordingly, the embodiments shownherein comprising a non-uniform cross-section are intended to clarifythe invention and should not be interpreted as limiting the scope of theinvention to a non-uniform cross-section. The lobes 40 (and the liner36) are helically formed along a selected length of the external tube 38such that the liner 36 conforms to the helically shaped inner surface 44so that the at least two lobes 46 formed on the shaped inner surface 44correspond to the lobes 40 formed in the liner 36. The external tube 38,including the inner surface 44, may be helically shaped by any meansknown in the art including machining, hydroforming, extrusion, and thelike. Shaping of the inner surface 44 of the external tube 38 isdescribed in co-pending U.S. patent application Ser. No. 10/056,135filed on Jan. 24, 2002, and assigned to the assignee of the presentapplication.

In some embodiments, the shaped inner surface 44 of the external tube 38is adapted to provide additional support for the liner material. Theshaped inner surface 44 “stiffens” the liner 36 by providing support forthe liner 36 (e.g., by forming a metal backing), thereby increasingpower available from the PDM. For example, shaping the inner surface 44to form a contoured backing for the liner 36 may stiffen the linermaterial proximate the lobes 40 by reducing an amount by which the liner36 may be compressed when contacted by the rotor 44 so that a betterseal may be formed between the rotor 44 and the stator 32. Moreover,reduced flexibility increases an amount of torque required to stall thePDM. The thickness 42 of the liner 36 is substantially uniform through across-section thereof. The shaped form of the inner surface 44 typicallyresults in a thinner liner 36 than is commonly used in prior art stators(such as that shown in FIG. 2). Fluid pressure is less likely to deformthe liner 36 and, accordingly, the liner 36 is less susceptible todeformation that could reduce the efficiency of the seal formed betweenthe rotor 34 and stator 32 (thereby producing an additional loss inpower output of the PDM 30).

The liner 36 may be formed from different materials, including but notlimited to resilient materials such as elastomers, polymers, and othersynthetic or natural materials known in the art. A preferred embodimentcomprises a liner 36 formed from a fiber reinforced elastomer material.However, while a preferred embodiment comprises an elastomer material asthe resilient material, any suitable resilient material known in the artmay be used within the scope of the invention. Accordingly, descriptionsof embodiments contained herein that refer to elastomer materials arenot intended to be limiting with respect to the type of resilientmaterial.

FIGS. 5-8 show an example of a method by which a fiber reinforced linerfor a stator may be formed. As shown in FIGS. 5 and 6, alternatinglayers of a resilient material, such as an elastomer material, and awoven fiber material may be overlaid so as to form a compositestructure. Note that some embodiments may include wrapping successivelayers over a core or mandrel. However, a mandrel is not necessary toform the liner. For example, a first layer comprising an elastomermaterial 50 (or, for example, an elastomer tube) may be wrapped with asecond layer comprising a fiber layer 52, which in some embodiments maycomprise a woven fiber mesh. In some embodiments, the fiber layer 52 maycomprise aramid fibers such as those sold under the mark “Kevlar” (amark of E.I. Dupont de Nemours of Wilmington, Del.), wherein the Kevlarfibers are wound at selected angles with respect to, for example, alongitudinal axis 54 of the liner (e.g., a longitudinal axis of thestator).

Other embodiments may comprise glass, carbon, or any other type ofsuitable fiber known in the art. Moreover, the fibers used to reinforcethe elastomer material 50 in a preferred embodiment are generally notimpregnated with a resin or other polymeric material, but it is withinthe scope of the present invention to use impregnated materials. Thefibers may also be wound directly onto the elastomer materials usingmeans known in the art, and use of a pre-woven cloth is not intended tolimit the scope of the invention.

Embodiments of the invention may comprise any number of layers andarrangements of elastomer and fiber reinforcing materials. FIG. 6 showsan embodiment comprising a fiber reinforcing layer 52 disposed betweentwo elastomer layers 50. However, a plurality of fiber reinforcinglayers 52 may be used so as to, for example, increase a stiffness and/orwear resistance of the liner. Moreover, the invention is not limited tothe layering techniques shown in FIGS. 2 and 3. For example, FIG. 9shows an embodiment comprising adjacent fiber layers 52 enclosed withinelastomer layers 50. This layering technique may be used to, forexample, increase fiber density. Additionally, a plurality of elastomerlayers may be used to form the liner. A preferred embodiment comprises aplurality of consecutively layered elastomer and fiber materials.

Fibers in the reinforcing layers may be wound at any angle with respectto the longitudinal axis of the stator. In some embodiments, the fibersmay be woven into a mesh, braided, or overlaid. For example, a pluralityof fibers may be woven together with approximately half of the fiberswound at an angle of +45 degrees and approximately half of the fiberswound at an angle of −5 degrees. Moreover, adjacent fiber layers may bewound at similar or different angles so that, for example, one fiberlayer provides circumferential support (e.g., a radially wound layer)and another fiber layer provides increased bending stiffness (e.g., alongitudinally wound layer).

In some embodiments, different elastomers and different fiber materialsmay be used in consecutive layers. Referring to FIG. 10, someembodiments may comprise first 60, second 62, and third 64 elastomerlayers enclosing first 66 and second 68 fiber layers. In someembodiments, the elastomer layers 60, 62, 64 may comprises the samematerial while the first 66 and second 68 fiber layers are formed fromKevlar and glass fibers, respectively. Alternatively, differentelastomer materials may be used to form the different elastomer layers60, 62, 64. Additional fiber layers may be included to, for example,form external layers that enclose the elastomer layers. Any combinationof materials may be used to form the layers, and the example shown inFIG. 10 is not intended to limit the scope of the invention.

In other embodiments such as the embodiment shown in FIG. 11, a windangle β of selected fibers 70 may be oriented relative to lobes 72formed on a liner 74 and shaped inner surface (not shown separately inFIG. 11) of the stator (not shown separately in FIG. 11). Note that FIG.11 shows a planar projection of a section of the liner 74 and includes astator axis 78 as a reference. For example, contact between the rotorand the stator generally occurs in a plane 76 (e.g., a “contact plane”)that is generally defined as a function of the helical shape of therotor and the stator. Accordingly, the fibers 70 may be wound (or apre-woven cloth positioned) so that the fibers 70 lay at a selectedangle β with respect to the contact plane 76. In this manner, the fibers70 may be positioned so as to improve the wear and performanceproperties of the lobes 72 in the region proximate the seal formedbetween the rotor and the stator. Note that the fibers 70 are shown asbeing positioned substantially perpendicular to the contact plane 76.This arrangement is shown to clarify the invention and is not intendedto be limiting.

Referring to FIG. 7, after the layering process has been completed, asubstantially cylindrical liner 80 may be inserted into a stator 82comprising a shaped inner surface 84 as described above. Referring toFIG. 8, ends of the stator 82 may then be sealed (using, for example,end pieces 86, 88) and the liner 80 may be cured by applying highpressure and high temperature to the interior of the liner 80 so as toexpand the liner 80 within the stator 82 so that the liner 80 mayconform to the shaped inner surface 84. A curing pressure, temperature,and time may be selected using means know in the art so as to completelycure the elastomer. After completion of the curing process, the statorwill be returned to normal atmospheric conditions. Final machining maybe required to complete the stator (e.g., ends of the liner 80 may needto be trimmed, ends of the stator 82 may be threaded, etc.).

During the curing process, the elastomer will typically plasticallydeform and conform to the shaped inner surface of the stator. Moreover,the elastomer may be selected so that, for example, the elastomermaterial “flows” to locally encapsulate the fiber layers and, in someembodiments, the individual fibers. The fiber layers may be wound orpositioned in a manner that allows the fiber layers to unwrap or expandso as to conform to the expansion of the elastomer material. Note thatan adhesive material may also be used to bond the liner to the innersurface. However, the type of elastomer may be selected so that anadhesive is not required. If an adhesive is required, any suitableadhesive known in the art may be used in the curing process.

Another embodiment comprising at least one aspect of the presentinvention is shown in FIG. 12. A lined rotor 100 may be formed byconsecutively layering elastomer layers 104, 108 and fiber layers 106over a rotor 102 to form a rotor liner 110. As described with respect toprevious embodiments, a plurality of elastomer and fiber layers may beused to form the rotor liner 110, and the layers may be arranged in anymanner to achieve, for example, a desired wear resistance, flexibility,stiffness, and the like. Moreover, the rotor liner 110 may be formedaccording to the other methods and embodiments disclosed herein suchthat the arrangement shown in FIG. 12 is not intended to be limiting.For example, the rotor liner 110 may comprise a substantially uniform ora non-uniform cross-section, and the elastomer and fiber layers may beformed according to the description of the previous embodiments.

After the rotor 102 has been coated with the fiber reinforced rotorliner 110, the rotor liner 110 may be cured by applying high temperatureand high pressure in a manner similar to that described with respect tothe embodiment shown in FIG. 7. The rotor liner 110 may be positioned onthe rotor 102 before curing so that the rotor liner 110 substantiallyconforms to an outer surface 120 of the rotor 102. The rotor liner 110may then be cured on the rotor 102 so that the fiber and elastomerlayers conform to the shape of the rotor 102 and form a bond with eachother and with the outer surface 120. This arrangement eliminates theneed for an intermediate forming apparatus (e.g., a mandrel) and permitsthe fiber reinforced rotor liner 110 to be compression molded directlyonto the outer surface 120 of the rotor 102 during the curing process.

After completion of the curing process, the lined rotor 100 may bereturned to atmospheric conditions and machined as required to achieve adesired final configuration. Referring to FIG. 13, the lined rotor 100is adapted for use with a stator 112 comprising a shaped, unlined innersurface 114. The operation of a positive displacement motor 116 formedby the lined rotor 100 and the shaped stator 112 is similar to thatdescribed with respect to previous embodiments. The lined rotor 100nutates within the shaped stator 112, and the rotor liner 110 iscompressed when lobes 118 formed on the lined rotor 100 contact theinner surface 114 of the shaped stator 112.

In a preferred embodiment of the invention, a fiber density issubstantially uniform throughout the thickness of the liner. A uniformfiber density is advantageous because it helps achieve, for example,uniform wear resistance throughout the thickness of the liner. A uniformfiber density is particular desirable proximate the lobes because thelobes experience the highest mechanical and thermal stresses. Additionalsupport and wear resistance proximate the lobes helps increase thelongevity of the liner. Note that, in some embodiments, the linerthickness is at a maximum proximate the lobes, and a uniform fiberdensity supports and helps stiffen these regions so as to reducedeformation of the lobes caused by, for example, fluid pressure andcontact with the rotor.

The stator and rotor forming processes described herein enable theformation of preferred embodiments (e.g., embodiments comprising linershaving a substantially uniform fiber density) because the formingprocesses help ensure that a desired fiber arrangement is maintained(after the application of heat and pressure to cure the stator or rotorliner). Accordingly, the stator and rotor forming processes help avoidlocal and global deformation of fibers disposed in the liner such asthat associated with elastomer injection around a set of prepositionedfibers in a stator tube.

Referring again to FIG. 4, the thickness 42 of the liner 36 may beselected to generate a desired amount of contact (or, if desired,clearance) between the liner 36 and the rotor 34. For example, thethickness 42 of the liner 36 may be selected to form a seal between therotor 34 and the stator 32 while maintaining a desired level ofcompression between the rotor 34 and stator 32 when they are in contactwith each other. Moreover, the thickness 42 of the liner 36 may beselected to permit, for example, swelling or contraction of the liner 36caused by elevated temperatures, contact with drilling fluids and otherfluids, and the like. Similar liner thickness selections may be madewhen forming a fiber reinforced rotor such as that shown in FIGS. 12 and13.

Note that the embodiment shown in FIG. 4 is generally referred to as a“5:6” configuration including 5 lobes formed on the rotor and 6 lobesformed on the stator. Moreover, the embodiment shown in FIG. 13 issimilarly referred to as a “4:5” configuration. Other embodiments mayinclude any other rotor/stator combination known in the art, including1:2, 3:4, 7:8, and other arrangements. Moreover, as described above,stators may generally be formed using “n+1” or “n−1” lobes, where “n”refers to a number of rotor lobes. Accordingly, the embodiments shown inFIGS. 4 and 13, and other embodiments described herein, are intended toclarify the invention and are not intended to limit the scope of theinvention with respect to, for example, a number of or arrangement oflobes.

Advantageously, the invention comprises a stator or rotor comprising adurable liner comprising a fiber reinforced material. The fiberreinforced liner material may be used with conventional rotors andformed stators having a shaped inner surface, and the liner material maybe adapted to form either a non-uniform or a substantially uniform linerthickness. The fiber density may be controlled so that it issubstantially constant through a cross-section of the liner material(especially proximate lobes formed in liner having a non-uniformcross-section), and the liner material may be formed using industrystandard manufacturing processes, such as calendaring, before beingdisposed in the stator or on the outer surface of the rotor.

The fiber reinforced liner material helps increase the longevity of theliner and, therefore, the stator or rotor by providing additionalmechanical and thermal support through the liner but especiallyproximate the stator or rotor lobes. Increased longevity reduces anumber of trips required to replace failed power sections when drillingwells in earth formation. Accordingly, fiber reinforced stators orrotors may significantly reduce the costs associated with drilling andexploration.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A method of forming a liner on a rotor for a positive displacementmotor, the method comprising: forming a liner on the rotor by layeringat least two resilient layers and at least one fiber layer on an outersurface of the rotor, the at least two resilient layers positioned so asto enclose the at least one fiber layer, the rotor comprising at leastone radially outwardly projecting lobe extending helically along aselected length of the rotor; and curing the liner on the rotor so thatthe liner conforms to the at least one radially outwardly projectinglobe formed on the rotor and to the helical shape of the rotor, thecuring adapted to form a bond between the liner and the outer surfaceand between the at least two resilient layers and the at least one fiberlayer.
 2. The method of claim 1, wherein the at least one fiber layercomprises a plurality of fibers wound at a selected angle with respectto a longitudinal axis of the rotor.
 3. The method of claim 1, whereinthe at least one fiber layer comprises a plurality of fibers wound at aselected angle with respect to the at least one radially outwardlyprojecting lobe.
 4. The method of claim 1, wherein the at least onefiber layer comprises aramid fibers.
 5. The method of claim 1, whereinthe at least one fiber layer comprises a plurality of fibers selectedfrom the group consisting of glass fibers and carbon fibers.
 6. Themethod of claim 1, wherein the at least one fiber layer comprises awoven fiber mesh.
 7. The method of claim 1, wherein the at least onefiber layer comprises a plurality of fibers wound directly onto at leastone of the at least two resilient layers.
 8. The method of claim 1,wherein fibers forming the at least one fiber layer are braided.
 9. Themethod of claim 1, wherein fibers forming the at least one fiber layerare woven.
 10. The method of claim 1, wherein the curing comprisesapplying a selected heat and a selected temperature to the rotor for aselected time period.
 11. The method of claim 1, further comprisingcoating an inner surface of the liner with an adhesive adapted to bondthe liner to the outer surface of the rotor.
 12. The method of claim 1,wherein the forming comprises positioning the at least one fiber layerso as to form a substantially uniform fiber density throughout the linerafter the curing.
 13. The method of claim 1, wherein the formingcomprises positioning at least two external fiber layers so as toenclose the at least two resilient layers.